The problem has been lurking over their heads through two rounds of the NBA playoffs over the past month.

Winners of a league-best 31 regular-season road games, the Boston Celtics have lost their touch during postseason travels, going a head-scratching 0-6.

Thanks to the comfort zone that is home-court advantage, though, the Celtics managed to survive that problem against the Atlanta Hawks and Cleveland Cavaliers.

Now, that security blanket has been taken away from the Celtics.

Now, they must break through on the road at least once against the Detroit Pistons during the remainder of the Eastern Conference finals, or the season will soon come to an end.

The home-court edge the Celtics earned by going 66-16 disappeared Thursday night when the Pistons grabbed Game 2, 103-97, to even the best-of-seven series.

The Celtics will have two shots to regain that home-court advantage on Memorial Day Weekend in Auburn Hills, Mich., and the pressure rests heavily on their shoulders to end those road woes now.

“Either (win on the road) or go home,” said center Kendrick Perkins. “We do have to win one on the road now. Nobody said it was going to be easy. It’s the Eastern Conference finals. We’ve just got to make sure we stick together and do what we do to get wins.”

Said Kevin Garnett, “There (was) going to come a time where we’ve got to get one, and we’ve finally come up front with that dilemma. We’ve got to find some way to win one on the road, and that’s what it is.”

The Celtics have been put in that situation because of a sub-par defensive effort in Game 2 when the Pistons became the first opposing team since the Utah Jazz on March 14 — and sixth all season — to break 100 points at the Garden.

The usual stifling defense the Celtics play at home wasn’t on display, and their 15-game Garden winning streak — including nine in the playoffs — was brought to a halt.

The Pistons, who grabbed the lead for good with 5:22 left in the third quarter, bounced back from their struggles in Game 1 with Richard Hamilton (25), Chauncey Billups (19), Antonio McDyess (15), Tayshaun Prince (14) and Rasheed Wallace and Rodney Stuckey (13 each) all hitting double figures.

“I thought we were a step slow in the rotations,” said Garnett, who had 24 points and 13 rebounds. “I thought, responsibility-wise, we slipped a couple of times. When we needed stops, man, we just couldn’t get that one stop to get over the hump.”

Said Coach Doc Rivers, “I never thought we put as much pressure defensively on them as we did in the first game. Usually, when we shoot basically 49 percent and score 97 points, we win games. Tonight, our defense just wasn’t as good as it’s been.”

Page 2 of 2 - Even a revived Ray Allen (25 points on 9 of 16 shooting) and an early third-quarter spurt with the crowd roaring couldn’t get the Celtics going.

They made bids in the fourth quarter, getting the Pistons’ lead to two points, but whenever a defensive stop was needed, it wasn’t there. A classic example came with 18.7 seconds left when the Pistons, with three seconds left on the shot clock, got a reverse layup from Billups on an out of bounds play to make it 100-94.

“Down the stretch, we came out and scored out of every timeout except for the last play when it was desperation,” said Rivers. “The problem is they came out and scored after every one, too.”

This afternoon, the Celtics will board a plane for Michigan knowing that if the road losing streak extended by two more games on the weekend, they will be facing a 3-1 deficit.

“This is the test for us,” said Allen. “We talked about all the things that happened in the first two rounds and now we’re in the situation where we can’t move on without winning on the road.

“Everybody in the locker room needs to knows that. The focus has to go up another notch.

“They’re definitely going to be rowdy (at The Palace of Auburn Hills). Detroit, historically, has been a tough building to play in.

They’ve always played well at home, so we have our work cut out for us. It’s not going to be easy. It’s going to take our best effort.”